Go to device manager (Press START and BREAK together), select Hardware, device manager.Have a look to see if any of the devices have a Yellow cross on them, if so highlight that item, right click and select disable.
Select any other item and go to the top and select ACTION , scan for hardware changes.

This will force the system to re-check and if necessary re-install the device.

Friends, sorry for long silence. I went to Device Manager to try your solutions. I saw things (entries) for USB under "+ USB controllers" in Device Manager. They are listed as follows:
- Unknown device (this is listed 2 times)
- USB Root Hub (this listed 5 times)
- VIA Rev 5 or later USB Universal Host Controller (this is listed 4 times)
- VIA USB Enhanced Host Controller
The only USB device permanently connected to the CPU is the printer but it does not show in Device Manager. I put a memory stick (Flash 2.0) into a USB port; it initially recognized it even though it could not open some files in it, and later reporting that the files are corrupt. I thought the printer and the memory stick should have have been picked up and listed in Device Manager under " + USB conrollers"? Please help. Thx.

I tried reformatting the stick (drive F on my laptop). Half-way thru, it reported that "Windows was unable to complete this format". I restarted the process but Windows reported that "This disk is write-protected". I right-clicked the stick (removalbe disk) and clicked properties to change read/write attributes, but there was no provision for that below the little properties window; it was blank. How do I remove the write protected attribute to enable me to re-format again? Thanks.